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Gates and Vents.

ilding is an.

to hold the
ince, and of
aced in the
the line P P,
i dusting of
md fastened
*11 together.
taken away,
nt from the
rhich is oak
here, pease-
of the sand

1 blackening
uld it would
jgh casting,
is a decided
lackening is
.nd so forms
ig being the

inished, and

2  now to be
of wood are
DW removed.
re used ; as

of the sand
icilitate the

taken from

the cupola in ladles, as already described, pour it simultaneously
into the  gates   of the mould,  and the sand  being   afterwards

broken away, reveals the cast-
ing, which has filled the matrix
left by the pattern.

As regards the proper posi-
tion in which to lay the pattern,
a little thought is necessary, but
as a general rule the most un-
important part of the casting
should be upward, that being
the part to which the scum and
impurities rise. If possible, the
scum should be entirely re-
moved from the mould itself,
being allowed to fill a large
gate or projection. This is
especially done in the case of
steam cylinders, where purity
is a necessity. Gates should be
as central as possible, and have
their mouths a little higher than
the mould, but they should, as
a rule, enter the latter low down,
particularly in deep castings, in
order that the air may be made
to pass out at the vent holes ;
but much judgment has to be
exercised; and in most cases
they should be placed a little on
one side, namely, not to enter
on the top" surface, otherwise
the corners of the sand may be
knocked off by the force of the
flow; and finally, they should
be put where shrinkage is likely to occur, that they may tend to
. fill up any shrinking portion.           :

Our next example shall be a Hand Wheel for a large stop